1. Field of the Invention
The invention relates to motor-assisted user-propelled vehicles such as an electric motor assisted bicycle. More specifically, the invention concerns an energy management system that controls the positive or negative motor output of the vehicle.
2. Background Art
Cycling is a very popular sport and has the main advantage of being an environmentally friendly mode of transportation and a very good way to maintain one's physical shape. The use of an electric motor to assist a man in propelling a bicycle is well known and has been introduced in the North-American market several years ago.
In going up a steep hill, the consumption of energy of the cyclist is increased dramatically since the energy required to fight against the gravity is increased. Increased energy consumption is also observed in the presence of an opposing wind. With the use of a power-assisted bicycle, a user can overcome such difficulties by commanding an electric motor to assist him in pedaling. Of course, using an electric motor means using a battery to supply power. Since batteries are generally quite heavy for their size and their energy storage capacity, one of the main challenges in the field of power-assisted cycling is to reduce the battery weight, while maintaining or increasing its energy storage capacity.
Aside from battery innovations, one attempt to overcome the weight/capacity problem has been to use an electric motor which can also work as a generator. When functioning in generator mode, the electric motor offers pedaling resistance to the user, converts the cyclist's energy to electric energy and uses the electric energy to recharge the battery. By recharging the battery while going down a hill, and using some power to go up, some of the energy is reused and the total energy consumption is lowered, which makes the battery last longer.
In order to determine the motor assistance or resistance, most prior art electric bicycles rely on a user activator. Similarly to how one changes the gears, the user increases or decreases the assistance or resistance level of the electric motor to suit his needs. The main problem with a fixed assistance level is that the user is not required to supply effort in order to propel the bicycle, and the bicycle may be considered to be a motor vehicle like a scooter.
To overcome this problem, some systems provide an assisted propulsion proportional to the user effort. The user effort is measured by a strain gauge disposed on the rear wheel shaft of the bicycle. A command box is used to process the user effort data and to command the motor to output power proportionally to the user effort. For example, the setting for motor output could be 25, 50, 100 or 200% of the user effort, the desired percentage being inputted by the user. In this application, the bicycle is never the only power source for propelling the bicycle.
One disadvantage of using a strain gauge to measure the user effort is its ineffectiveness when installed on the front wheel of a bicycle. Since some types of bicycle models do not allow the electric motor to be installed on the front wheel, these systems can only be installed on traditional bicycle models.
The act of changing the assistance level, in the first case, or proportion in the latter case, is disturbing to a user. For example, if one needs to change both the gears of his bicycle and the motor assistance or resistance in a hill, he may have already slowed down by the time these two operations have been executed.
The motor-assisted user-propelled vehicles are very limited in the quantity and type of parameters that may be set for the motor output to adjust to. The use of an automatic throttle control to a desired speed, a fixed output control, and fixed output ratio offer limited control possibilities.